The invention relates to a pressure medium adjusting element with a lubricating valve. In a known pressure medium adjusting element of this type (German OS No. 28 02 676) an axial piston is designed in one piece with an annular pusher, concentric with respect to the shaft segment; said pusher cooperating directly with a radial shaft bore, when the clutch in its released position, to allow a throttled flow of lubricant to reach the disk stack and by increasing the flow by increasing the throttle cross section of the radial shaft bore when the clutch is in its engaged position.
In this known arrangement, relatively high torque losses occur when the clutch is released, due to the oil shearing forces prevailing at the disks as a result of the flow of lubricant. However, the volume of lubricant available per unit of time, when the clutch is engaged, is limited by the design characteristics of the shaft segment, so that when the clutch is engaged an increase in the amount of heat in clutch stack occurs which cannot be taken sufficiently into account.
German OS No. 32 20 746 teaches a lubricating device of a different species for a manual gear shift transmission, wherein a metering piston is held in one stroke end position by a spring force and is actuatable into its other stroke end position by an auxiliary force which are generated when shifting the transmission, to thereby press a volume of lubricant, drawn up into a spring chamber from an oil sump, through a first check valve into a second check valve and hence into a lubricating line which leads to the clutch and synchronizer units of the individual gears. In this lubricating device, high losses are caused by liquid friction and are unavoidable, because each time the gears are shifted, all the clutch and synchronizing components which are not involved are given lubricant.
An object of this invention consists in keeping the losses caused by oil shearing forces low when the clutch is released, by a pressure medium adjusting element with a lubricating valve for actuating a disk clutch, and supplying a sufficiently large quantity of lubricant to handle the increased amount of heat produced when the clutch is engaged.
On the basis of a pressure medium adjusting element with a lubricating valve wherein a piston is located in a cylinder for activating a set of clutch disks and wherein the piston controls a flow of fluid from a radial shaft segment, located internally of the cylinder and piston, to the stack of clutch disks by means of a lubricating valve controlling flow of lubricating oil from a shaft bore in the shaft segment, the object is achieved in an advantageous manner by locating a large pressure tight baffle chamber between the piston and the clutch disk and having the piston control flow of lubricating oil from a radial port in the shaft segment through the baffle chamber by having the piston activate a lubricating valve to control the flow of oil from the baffle chamber. The invention also includes a bias spring for the piston located concentrically with the valve. Additionally, the invention includes a equalizing chamber located between the valve outlet of the baffle chamber and the clutch disks.
The invention provides the following advantages:
The lubricant which is stored in the large baffle chamber and the equalizing chamber, when the clutch is released, is additionally available for carrying away heat when the clutch is engaged.
When the clutch is released, the flow of lubricant to the clutch disk stack through the lubricating valve is completely cut off so that the shear friction losses are negligible. This is important for the use of a planetary gear set which operates as an overdrive, wherein, when the disk clutch is released, the takeoff-side driving element is speeded up and the transmission element connected to the other half of the clutch is firmly braked, so that the mutual relative rpm of the two clutch halves is especially great. In addition, the frequency of shifting into a gear designed as an overdrive and the next direct gear is high and therefore it is especially necessary for heat to be carried away from the disk stack.
With the clutch engaged, by virtue of the volume of lubricant captured in the baffle chamber and equalizer chamber, equalization of centrifugal force is accomplished with respect to the volume of hydraulic oil stored in the working pressure chamber to energize the axial piston.
Cutting off the flow of lubricant to the disk stack permits an increased flow of lubricant to the tooth engagement points of the corresponding planetary gear set. When the planetary gear set operates with a free-running clutch to make shifting easier, an increased flow of lubricant to improve the lubrication of the free-running clutch is obtained.
A separate closing spring for the lubricating valve is rendered unnecessary by using the return spring on the axial position.
The lubricating valve operates as a seat valve and therefore, even after a small piston travel of the axial piston, supplies a sufficient flow of lubricant to the disk stack when the clutch is engaged.
These and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which show, for the purposes of illustration only, one embodiment in accordance with the present invention, and wherein: